Note 6 — REMARKS, ON A PAMPHLET, &c.

In the fifth Volume of M. De La Caille’s Ephemerides, Page 31, he says, “that any Person would be in the wrong to suppose that the Longitude at Sea can be determined by the Moon, to a less Error than two Degrees, let the Method which is employed be never so perfect, let the Instruments, of the Sort now in use, be never so excellent, and let the Observer be the most able and accomplished. For if we examine, without prejudice, all the Circumstances which enter into the Calculation and into the Observation of a Longitude at Sea, we shall be easily convinced, that it would be ridiculous to maintain, that the Sum of the inevitable Errors should not amount to five Minutes of a Degree, that is, to two Degrees and a half of Longitude.” N. B. M. de la Caille published this in the Year 1755, and is universally allowed to have been an excellent Observer, and made several Voyages by Sea, where he made Trials of this Method by the Moon.

Dr. Halley and Dr. Bevis (as appeared to the Honourable House of Commons upon an Examination of the latter) did, with an excellent Hadley’s Quadrant, rectified by Mr. Hadley himself, and in his presence, attempt to take the angular Distance of the Moon from Aldebaran, a Star of the first Magnitude; but with such bad Success (some of the Observations removing Greenwich from itself almost as far as Paris) that Dr. Halley seemed to be out of Hope of obtaining the Longitude by this Method.